On Tuesday, 9 June 2015 at 23:04:41 UTC, Andrei Alexandrescu
wrote:
On 6/9/15 3:58 PM, Timon Gehr wrote:
On 06/09/2015 05:28 PM, Andrei Alexandrescu wrote:
Following the use of This in Algebraic
(https://github.com/D-Programming-Language/phobos/pull/3394),
we can
apply the same idea to Tuple, thus allowing one to create
self-referential types with ease.
Consider:
// A singly-linked list is payload + pointer to list
alias List(T) = Tuple!(T, This*);
// A binary tree is payload + two children
alias Tree(T) = Tuple!(T, This*, This*);
// or
alias Tree(T) = Tuple!(T, "payload", This*, "left", This*,
"right");
// A binary tree with payload only in leaves
alias Tree2(T) = Algebraic!(T, Tuple!(This*, This*));
Is there interest in this? Other application ideas to
motivate the
addition?
Andrei
Well, the issue is with this kind of use case:
alias List(T)=Algebraic!(Tuple!(),Tuple!(T,This*));
So a list is either nothing, or a head and a tail. What is the
problem here? -- Andrei
The `This*` here is not mapped to
`Algebraic!(Tuple!(),Tuple!(T,This*))` - it's mapped to the
closest containing tuple, `Tuple!(T,This*)`. This means that the
tail is not a list - it's a head and a tail. The list is either
empty or infinite.
At any rate, I think this feature is useful enough even if it
doesn't support such use cases. You can always declare a list as
a regular struct...
